Washington, DC – Sea-level rise—a growing threat that washes away beaches, attacks costal development, and raises the platform for launching ever more damaging and deadly storm surges—can be cut significantly by reducing local air pollution from black carbon, methane, and tropospheric ozone, along with factory-made coolants called HFCs.

This is the conclusion of a multi-year research effort led by Professor V. Ramanathan at Scripps Institution of Oceanography, University of California, San Diego, to be published online 14 April by Nature Climate Change. The study calculated that the annual rate of sea-level rise could be reduced up to 24% by 2100 by controlling these four climate pollutants, and that cumulative sea-level rise could be reduced by 22%.

‘It is still not too late to avoid disastrous climate changes,” stated study-lead, Dr. Ramanathan. “If we stabilize CO2 concentrations below 450 ppm by 2100 and simultaneously reduce SLCPs, we can limit the end-of-century warming by 50% and keep below the 2°C (3.6°F) safety guardrail, from the projected 4°C (7.2°F).”

These four climate pollutants are collectively known as “short-lived climate pollutants” because they clear out of the atmosphere in a matter of days to a decade and a half. Previous research by Dr. Ramanathan and a follow-on study by the United Nations Environment Programme & the World Meteorological Organization showed that cutting SLCPs, using existing technologies and institutions in most cases, can cut the rate of climate change by half or more by mid-century.

The current study calculates the significant additional benefits that SLCP mitigation can provide by the end of the century—a critical 1.1°C reduction in future warming. This is the same avoided warming aggressive carbon dioxide mitigation can produce in this period. Cutting both SLCPs and CO2 can avoid 2.3°C of warming and keep the Planet under the 2°C guardrail according to the study, and reduce the rate of sea-level rise by up to 50%, with SLCP’s providing two-thirds of the reductions.

“Combined mitigation will reduce the cumulative sea level rise by about 30% (from the projected 0.5 m to 2 m/ 1.5 ft to 6.2 ft),” added Dr. Ramanathan. “It is encouraging that SLCPs contribute about half of the warming reduction and about two-thirds of the sea level rise reduction, since we have technologies to reduce them. Without CO2 stabilization below 450 ppm, however, both the warming and sea level can rise to dangerous levels beyond 2100."

The damage from rising seas and higher storm surges is one of the most visible and costly effects of climate change. Populations and infrastructure of coastal cities will become more vulnerable to flooding and storm surges, which are also expected to become more frequent and stronger as global temperatures rise. Indirect impacts can include impacts on job markets and tax revenue, and changes in population and migration. According to a 2010 OECD study, a rise in sea-levels of only three feet (1 meter) by 2070 puts at risk 150 million people and $35 trillion in assets in just 20 of the world’s most vulnerable and fastest growing port cities, more than half of which are in developing Asian countries.

“This ground-breaking study provides the blueprint for climate justice this century,” stated Durwood Zaelke, President of the Institute for Governance & Sustainable Development. “Cutting these air pollutants and chemical coolants can cut warming in half for many decades, and is essential for protecting vulnerable people and places this century,” he added. “Failure to cut SLCPs will halt the impressive gains in poverty reduction of the past few decades,” Zaelke said, “and drive millions more into extreme poverty.”

Because three SLCPs are potent air pollutants, cutting them can save millions of lives every year, while significantly increasing crop yields, making this important for promoting sustainable development. In South Asia, for example, air pollution is the leading preventable cause of disease, according to a recent report by the World Health Organization.

"We need an all of the above approach to controlling greenhouse gases. Cutting carbon emissions is critical, but we also need to take advantage of the very substantial short term gains that can be achieved by cutting emissions of non-carbon climate pollutants," stated study co-author Claudia Tebaldi of Climate Central. “Readily achievable reductions of non-carbon dioxide pollutants would do far more to slow sea level rise this century than actions to reduce carbon emissions alone, protecting millions of people and billions of dollars of real estate from rising seas," she added.

Based upon data from the U.S. Geological Survey and NOAA, without engineering protection, five feet of sea-level rise could permanently flood 94% of Miami beach, 88% of New Orleans, 7% of New York City, 63% of Atlantic City, 20% of Jersey City, 68% of Galveston TX, 6% of San Francisco, and 4% of Seattle. Approximately 2.6 million homes and 5 million people reside on land less than four feet above high tide in the U.S.; approximately 50% of those people are in the state of Florida.

The study found that delaying mitigation of SLCPs by 25 years will decrease the impact of CO2 and SLCP mitigation, and will make it difficult if not impossible to keep warming below 2°C by the end of the century. Delayed action on SLCPs could increase sea-level rise by up to 11%.

The Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC) is the first-ever global effort specifically dedicated to reducing emissions of SLCPs, and has already undertaken seven fast-action initiatives designed to mobilize resources and accelerate global action on SLCPs.

The sea-level report drew heavily from the data collected by Project ABC, a United Nations sponsored study of pollution masses known as atmospheric brown clouds, which are especially prevalent in South Asia. SLCPs are the main component of brown clouds emitted primarily from biomass burning, diesel emissions, and methane from landfills.

The study co-authors include: Aixue Hu and Warren M. Washington of the US National Center for Atmospheric Research, and Yangyang Xu of Scripps Institution of Oceanography.